Single-crystal neutron spectrometer



Sept. 26, 1961 Filed Sept. 2, 1960 PRIMARY BEAM FROM REACTOR D. HOLCOMB 3,002,095

SINGLE-CRYSTAL NEUTRON SPECTROMETER 2 Sheets-Sheet 1 INVENTOR. David L. Holcomb \LO ATTORNEY Sept. 26, 1961 Filed Sept. 2. 1960 D. 1.. HOLCOMB 3,002,095

SINGLE-CRYSTAL NEUTRON SPECTROMETER 2 Sheets-Sheet 2 Hwy :2 iiim! milllll" INVENTOR.

David L. Holcomb 6a -4 4 MM ATTORNEY This invention relates generally to an improved apparatus especially useful in neutron spectrometry.

In conventional neutron spectrometers, a beam of neutrons from an atomic reactor is brought out through an aperture or beam hole in the reactor shield and caused to strike a crystal monoehromator. Neutrons are reflected from the crystal at dififerent angles, depending upon their wavelengths. The crystal must be surrounded by a shield, such as a concrete box to prevent undesired egress of the reflected neutrons and the shield .must have a channel to transmit the selected beam. The crystal is turned at various angles to the incident beam of neutrons and the shield must have a channel to transmit the selected beam out to the spectrometer. The crystal is turned at various angles to any fixed point of reference. Hence a single passageway in the concrete crystal shield is not suitable, and a moveable channel is desired. Such movement must not permit escape of neutrons, however.

The crystal is rotated in the plane of the incident neutron beam. Hence it is desirable to move the channel in the same plane. For simplicity and low cost, ordinary gears should be used, if practicable. Accordingly, it is the object of this invention to provide a channel in a reactor shield and means to move that channel in a selected plane, while maintaining the inner end of the channel focussed upon a fixed point.

Another object of the invention is to translate one end of a longitudinal tube along a given path while the central axis of the tube intersects a given point at all times.

These and other objects of the invention will become apparent from the following detailed description of a preferred embodiment thereof, when read together with the attached drawings, wherein:

FIG. 1 illustrates in a section a shielding plug including the collimating channel, and

FIG. 2 illustrates the driving mechanism for moving the channel.

Referring now to FIG. 1, a crystal 1 may be disposed inside an opening inside the crystal shield 2. An opening in the reactor shield 3 is provided with a large plug in the form of a stepped outer cylinder 4 approximating a cone. Disposed inside the outer cylinder and off-axis is a smaller inner stepped cylinder 5 also approximating a cone. A tube 6 forms a channel 7 ofi-axis of cylinder 5. The two stepped cylinders and the tube are so oriented that their central axes intersect at a common point at the center of the crystal. The stepped cylinders may be rolled mild steel, filled with concrete, or steelmicarta laminations bolted together, for example, serving as shielding to prevent escape of radiation, particularly neutrons, to the outside of the reactor shield. If the device were to be used where no shielding were required, the stepped cylinders could be replaced by cones.

Referring to FIG. 2, the outer extremity of cylinder 4 is provided with external teeth 4A around its periphery to engage a spur or drive gear 8, which is fixedly mounted on a plate 9. A gear sector is also fixed to and carried by plate 9 and is provided with an internal arcuate portion 10A which serves as a stationary gear. The center of the arcuate portion lies on the axis of cylinder 4. A gear 5A is fixed to the external end of cylinder 5 States Patent "are and is provided with teeth to engage gear 10A. The diameter of gear 5A is exactly one-half that of gear 10A, with gear 10A having twice the number of teeth per equal are as gear 5A.

- In operation, rotation of the drive gear 8 turns cylinder l and consequently, tends to rotate cylinder 5 about the axis of cylinder 4. Since gear 10* does not move, cylinder 4 will be rotated about its own axis simultaneously as it moves along the surface of gear 10. Such simultaneous rotation about two axes will cause the elf-axis channel 7 to move in a straight line, but the axes of both cylinders and the channel will continue to intersect at the center of crystal 1.

The outer cylinder gear may be 18 in. in pitch diameter, with teeth. The intermediate step on cylinder 4 may be 15 in. in diameter and the inner step 12% in. in diameter. The inner cylinder 5 may be 10 /2 in. in diameter at its outer portion, 8 /2 in. in diameter in the center, and 6 /2 in. in diameter at its inner portion. The inner part of channel '7 may be 2 in. in diameter, with the outer part being 2% in. in diameter. The gear 5A may be 7 in. in pitch diameter, with 84 teeth. The stationary gear '10 has twice the pitch diameter of gear 5A; that is, 14 in., with 72 teeth in 154. The spur gear 8 may be of any convenient pitch diameter and number of teeth, since it of course does not affect the movement of the channel 7.

By approriate selection of the ratio of diameters of gears 5A, 10A the path described by the external end of channel 7 may be an arc of a desired radius, rather than a straight line, across the external face of said plug 4. If cones are used rather than stepped cylinders, the external face of plug 4- would be the base of the largest cone.

It is to be understood that the above dimensions are given by way of example only and not in limitation of the scope of the invention.

Having described my invention, what is claimed as novel is:

1. Means for transmitting a beam of radiation from a point within a reactor through a surrounding shield to external utilization means comprising a first stepped cylindrical shielding plug disposed in said shield and provided with an oil-axis longitudinal passageway, the axes of said member and said passageway intersecting at said point; a second stepped, cylindrical shielding plug providedwith an oil-axis longitudinal channel, said second plug being disposed Within said passageway and fixed to said first plug to rotate therewith, the axis of said channel passing through said point; first gear means including a gear mounted to rotate about the axis of said first plug for rotating said first plug about its axis within said shield; a second gear carried by the outer end of and mounted to rotate about the axis of said second plug; and a fixed arcuate gear sector mounted concentric to the axis of said first plug and engaging said second gear to rotate said second member about the axis thereof while said second member is rotating about the axis of said first member, thereby translating said channel across said first plug.

2. The device of claim 1 wherein the diameter of said fixed gear sector is twice the diameter of said second gear to translate said channel linearly.

References Cited in the file of this patent FOREIGN PATENTS 1,169,763 France Sept. 15, 1958 1,157,964 France Aug. 17, 1959 

